1. Field of the Invention
The present invention relates to a purification treatment system for clean and sewage water and various kinds of discharge water, and relates in particular to an improvement in a water treatment in which a flocculant is applied.
2. Description of the Related Art
A flocculation treatment has heretofore been widely used in a purification treatment for clean and sewage water, and various kinds of discharge water. Also in a rapid filtration method and a membrane filtration method which are employed in general water purifying treatments, the flocculation treatment is applied except for some clear water sources. For example, in a water purification system [refer to “Water supply facility design guideline (2000 edition), Publication office: aggregate corporation Japan Water Works Association, Issue (second edition): June, 2000, 150 pages ((3) rapid filtration method), page 187 (5. 4. 3 flocculation basin)], illustrated in FIG. 3, a raw water 10, after running through a raw water tank 11, is injected with a flocculant 16 and mixed with it for about several minutes in a flush mixing tank 12, and then sent to a flocculation basin 13. Flocs grow larger as the flocculant injected water is slowly agitated in the flocculation basin 13. For this, it took 10 to 40 minutes.
Subsequently, treated water needs, for example, about 20 to 40 minutes to be sent to a sedimentation basin 14 for sedimentation and separation of bulky suspended solid (it is hereinafter referred to as SS), and small SS is filtrated in a next rapid filtration basin 15 and the like, thereby obtaining a filtrate 17. In addition, this filtrate 17 may sometimes be further subjected to a advanced treatment as necessary.
The coagulation treatment in such a water purifying treatment is for flocculating small SS particles and polymer dissolving components for easy separation. First, in the flush mixing tank 12, if the flocculant such as aluminum sulfate or poly aluminum chloride is injected into raw water and agitated, the minute SS particles and the like are electrically neutralized, thereby forming micro flocs. Then, this flocculant injected water is agitated by a system such as a mechanical agitating system or bypass flow system with an adjusted agitation intensity in the flocculation basin 13, which is set to grow the flocs larger so that they will have a size suitable for a subsequent sedimentation treatment, but there is a limitation in treatment capacity per facility area, making it difficult to reduce size.
On the other hand, as membrane filtration capability is being remarkably increased with technical development in ceramic membrane filtration, a membrane apparatus itself can be significantly reduced in size, but because a flush mixing tank and the flocculation basin require an equipment scale proportionate to a water formation amount, there has been a disadvantage that the equipment can not obtain a merit of scale if it is scaled up.